Vogelstein et al. have examined chromosomes in familial polyposis patients from the benign adenoma stage to the cancer stage and have detected the disappearance in heterozygosity (deletion of allele) in chromosomes 5, 17, 18 and 22 (New Engl. J. Med., 319, 525-532, 1988), thus indicating the possible existence of a familial polyposis-related tumor suppressor gene in these deleted chromosomes. Thereafter, it was confirmed that the tumor suppressor gene located on chromosome 17P was identical with the P53 gene, a known oncogene (Science, 244, 217-221, 1989). Subsequently, a DCC (deleted in colorectal carcinoma) gene was identified as a tumor suppressor gene located on chromosome 18q (Science, 247, 49-56, 1990), and the isolation of a MCC (mutated in colorectal cancer) gene and an APC (adenomatous polyposis) gene located on chromosome 5q was reported (Science, 251, 1366-1370, 1991; and Science, 253, 665-669, 1991).
The DCC gene has a considerably large size (2 to 3 mega bases), and a cloned 370 kb fragment thereof is considered to have at least 8 exons. The corresponding mRNA is from 1 to 12 kb, and its expression has been found in the large intestine, the brain and the like. In large bowel cancer cells, it has been confirmed that certain mutations such as deletions, point mutations, insertions and the like occur in the DCC gene. In the future, the function of the DCC gene as an antioncogene will be elucidated, for example, by introducing the DCC gene into DCC gene-deficient cancer cells.
It is presumed that the function of the peptide encoded by the DCC gene (referred to as "DCC gene product" hereinafter) involves intercellular communication, because its deduced amino acid sequence shares homology with a cell adhesion molecule, N-CAM (neural cell adhesion molecule). However, many aspects of the localization, function and the like of tile DCC gene product are still unclear because of the lack of availability of antibodies which react specifically with the DCC gene product.
Antibodies specific for the gene product of the tumor suppressor gene P53 located on chromosome 17P have been prepared (Eur. J. Biochem., 159,529-534, 1986), and it has been reported that cancer cells expressing large quantities of the P53 gene product stain positive using the abovedescribed antibodies in an immunohistochemical staining protocol (Proc. Natl. Acad. Sci. USA, 87, 7555-7559, 1990). In addition, it has been reported that a peptide encoded in the P53 gene (referred to as "P53 gene product" hereinafter) can be measured quantitatively by means of an enzyme immunoassay technique using antibodies to the P53 gene product (J. Cell Science, 101, 183-189, 1992).
Thus, the availability of antibodies specific for the DCC gene product would make possible not only immunohistochemical staining and quantitative determination of the DCC gene product but also cancer diagnosis and the like.